1. Field of the Invention
The present invention relates to an improvement in or relating to a crank angle detecting apparatus for an internal combustion engine.
2. Description of the Prior Art
It is customary in the art to detect the crank angle of an internal combustion engine for ignition and fuel injection control based on the detected value, to ensure smooth running of the engine. A relatively simple-structured crank angle sensor is usually employed for detecting the crank angle of the internal combustion engine.
The crank angle sensor produces crank angle signals C1 to C12 and first and second top dead center signals G1 and G2, for example, as shown in FIGS. 8(A) to 8(C). The crank angle signals C1 to C12 are each created whenever the internal combustion engine (the crankshaft) rotates through a fixed angle (30.degree. CA in this case). The first and second top dead center signals G1 and G2 are alternately produced at a predetermined position (at the top dead center in this instance) during each rotation of the internal combustion engine.
Conventionally the crank angle of the internal combustion engine is detected through use of such a crank angle sensor in the following manner. A counter is provided which is incremented by one upon each application of one of the crank angle signals C1 to C12 and is preset to "1" when supplied with one of the top dead center signals G1 and G2. Further, a decision means is provided to decide which of the first and second top dead center signals was applied when the counter was at its full count "12". The crank angle of the internal combustion engine is detected based on the result of decision by the decision means and the count value of the counter. For example, when the signals shown in FIGS. 8(A) to 8(C) are provided by the crank angle sensor, since the count value of the counter varies with the crank angle of the internal combustion engine, as depicted in FIG. 8(D), the crank angle can be obtained from the count value of the counter.
Fuel injection control and ignition control are carried out according to the count value of the counter and the result of the decision by the decision means. For instance, in the case of performing fuel injection control of a six-cylinder internal combustion engine, fuel is injected into first and fifth cylinders at the timing when the counter goes to "2" after the detection of the first top dead center signal G1, as indicated by FIG. 8(E); fuel is injected into third and sixth cylinders at the timing when the counter goes to "10" after the detection of the first top dead center signal G1, as indicated by FIG. 8(F); and fuel is injected into second and fourth cylinders at the timing when the counter goes to "6" after the detection of the second top dead center signal G2, as indicated by FIG. 8(G).
The above conventional method for the detection of the crank angle of the internal combustion engine for its fuel injection and ignition control, encounters the following problem. When noise is superimposed on the first or second top dead center signal G1 or G2, the count value of the counter does not agree with the actual crank angle of the internal combustion engine, and consequently, ignition and fuel injection control based on such a count value will not permit smooth running of the internal combustion engine. For example, in the event that noise (a) is superimposed on the top dead center signal G2, as shown in FIG. 8(C), the counter will go to "1" upon the occurence of the noise (a), as depicted in Fig. 8(H), so that the count value remains inconsistent with the crank angle until the top dead center signal G2 is applied next.
As a solution to this problem, the following arrangement has been proposed. It includes a counter which is incremented by one upon each application of one of the crank angle signals C1 to C12 shown in FIG. 8(A) and is preset to "1" upon application of one of the crank angle signals C1 to C12 when the counter is at the full count "12", and a decision means for deciding which of the first and second top dead center signals G1 and G2 was applied when the count value was "12". Ignition and fuel injection control takes place according to the result of the decision by the decision means and the count value of the counter. With such an arrangement, even if noise is superimposed on the first or second top dead center signal G1 or G2, the count value of the counter can be made to correspond to the crank angle of the internal combustion engine. For instance, even when the noise (a) is super-imposed on the second top dead center signal G2 shown in FIG. 8(C), the count value of the counter is "7" at the occurrence of noise and will not be preset by the noise (a) to "1". Thus the count value is always in agreement with the crank angle of the internal combustion engine.
However, the above prior art example has the following drawback. When noise is superimposed on the crank angle signals C1 to C12, since the count value of the counter and the crank angle of the internal combustion engine will not correspond semipermanently, ignition control and fuel injection control based on such a count value will not provide smooth running of the internal combustion engine. For instance, in the event that noise (b) is superimposed on the crank angle signals C1 to C12, as shown in FIG. 8(A), the counter goes up to "7" from "6" at the timing of generation of the noise (b) and goes to "1" upon application of the crank angle signal C12, as shown in FIG. 8(I). As a result, the count value of the counter semipermanently deviates from the crank angle of the internal combustion engine by 30.degree. CA. In other words, the count value of the counter is "1" at the occurrence of each of the top dead center signals G1 and G2 but the top dead center signals are neglected, resulting in a semipermanent deviation of 30.degree. CA between the count value and the crank angle of the internal combustion engine.
Furthermore, the two prior art examples described above are both defective in the following point, too. When noise is superimposed on the crank angle signal in the case where the first and second top dead center signals G1 and G2 cannot be detected as a result of bad contact or some other cause, the count value of the counter and the crank angle of the internal combustion engine will not correspond until the top dead center signals G1 and G2 can be detected again. Accordingly, ignition control and fuel injection control based on such a count value is likely to introduce troubles in the internal combustion engine, and will not allow smooth running thereof.